Given that both structures are similar, it follows that the ratio of their corresponding lengths are equal.
To find out what should be the correct length of AB that she should change to, set up the proportion showing the ratio of 2 corresponding lengths of both structures. Thus:
We will assume AB is unknown.
PR = 7.5 ft
AC = 2.5 ft
PQ = 6 ft
Plug in the values into the equation
Cross multiply
Divide both sides by 7.5
The architect should change the length of AB to 2 ft
To find out how much more does she spend on clothes that he does on movies, subtract the amount she spends on movies from the amount she spend on clothes
Simplify
therefore
She spends 1/3 more on clothes that he does on movies